Chase Whitley sat in the dugout after the fifth inning Thursday night, having not surrendered a run, before Dellin Betances got the final out. Finally, Whitey started to relax.

When asked what he felt, the right-hander said: “Relief.”

No doubt Joe Girardi felt the same thing after the Yankees 1-0 win over the Mets at Citi Field to get a split of the Subway Series.

“His performance was spectacular,” the manager said of Whitley’s 4 ²/₃ scoreless innings in his major-league debut.

The converted reliever was summoned from Triple-A Scranton/Wilkes-Barre to take the spot of CC Sabathia, who joined the growing list of starters on the disabled list.

Girardi said Whitley would remain among the starters, at least for now.

“We haven’t made a change in our rotation,” Girardi said. “He didn’t do anything not to start.”

Whitley said he was just pleased to get it over with.

“To put that one away and look forward to the next one — whenever that might be — it was a good day,” Whitley said.

He began to run out of steam in the fifth, as he issued his first two walks with one out in the inning to Ruben Tejada and Juan Centeno. After Mets starter Jacob deGrom bunted them over, Girardi decided to remove Whitley before facing the lineup a third time.

“We felt he tired,” Girardi said.

Whitley, who threw 74 pitches, agreed.

“The adrenaline wore off a little bit,” said Whitley, who also singled in his first at-bat. “It’s something I’ve got to build on for next time.”

Still, for a team that has seen its starting rotation go from deep to paper-thin in a matter of weeks, Whitley provided as much as they could have asked for.

With the way Sabathia struggled even before going to the disabled list with a bad right knee, the Yankees may have even signed up for Whitley’s outing even if the big lefty were on the mound.

So while Whitley — like David Phelps and Vidal Nuno — can’t replicate the performances expected from the injured Sabathia, Ivan Nova and Michael Pineda, the Yankees may be able to survive for a while if they get more innings like they did Thursday from Whitley.

And as his former SWB teammates said before he was called up, Whitley wasn’t overwhelmed by the scene.

“He didn’t show any nerves at all,” Brian McCann said. “He executed all his pitches.”